Dielectric isolated fin with improved fin profile

ABSTRACT

A method of forming a fin structure that includes forming a plurality of fin structures from a bulk semiconductor substrate and forming a dielectric spacer on a sidewall of each fin structure in the plurality of fin structure. A semiconductor spacer is formed on a sidewall of the dielectric spacer. A dielectric fill is formed in the space between the adjacent fin structures. The semiconductor spacer and a portion of the fin structures that is present below a lower surface of the dielectric spacer are oxidized. Oxidizing a base portion of the fin structures produces a first strain and oxidizing the semiconductor spacer produces a second strain that is opposite the first strain.

BACKGROUND

Technical Field

The present disclosure relates generally to semiconductor fabrication,and more particularly to structures and methods for forming fin fieldeffect transistors (FinFETs).

Description of the Related Art

With the continuing trend towards miniaturization of integrated circuits(ICs), there is a need for transistors to have higher drive currentswith increasingly smaller dimensions. FinFET technology is becoming moreprevalent as device size continues to shrink. However, the cost ofmanufacturing SOI finFETs can be high.

SUMMARY

In one embodiment, a fin structure is formed by a method that includesforming a plurality of fin structures from a bulk semiconductorsubstrate, and forming a dielectric spacer on a sidewall of theplurality of fin structure. A semiconductor spacer is formed on asidewall of the dielectric spacer. An exposed portion of the bulksubstrate that is present between the semiconductor spacers on adjacentfin structures is etched to form a pedestal portion of the bulksubstrate. A dielectric fill is formed in the space between the adjacentfin structures. The semiconductor spacer and a portion of the finstructures that is present below a lower surface of the dielectricspacer are annealed, wherein the annealing of the portions of the finstructures that are below the lower surface of the dielectric spacerproduces a first strain and annealing the semiconductor spacer producesa second strain that is opposite the first strain.

In another embodiment, a fin structure is formed by a method thatincludes forming a plurality of fin structures from a bulk semiconductorsubstrate. A first dielectric fill is formed in the space between theadjacent fin structures. The sidewalls of the upper portion of theplurality of fin structures are exposed. A dielectric spacer is formedon the exposed sidewalls of at least one fin structure in the pluralityof fin structure. A semiconductor spacer is formed on a sidewall of thedielectric spacer. A second dielectric fill is formed on the spacebetween the adjacent fin structures on the first dielectric fill. Thesemiconductor spacer and a portion of the fin structures that is presentbelow a lower surface of the dielectric spacer is annealed, whereinannealing the portion of the fin structures below the lower surface ofthe dielectric spacer produces a first strain and annealing thesemiconductor spacer produces a second strain that is opposite the firststrain.

In another aspect of the present disclosure, a fin field effecttransistor (finFET) is provided having a uniform tail region. In oneembodiment, the finFET includes a fin structure that is present on adielectric surface. The fin structure includes a uniform tail regionthat is present at an interface of the fin structure and dielectricsurface. A gate structure is present on a channel portion of the finstructure and includes a gate dielectric in contact with the channelportion of the fin structure and at least one gate conductor. A sourceregion and a drain region are present on opposing sides of the channelportion of the fin structure.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a side cross-sectional view of forming a plurality of finstructures from a bulk semiconductor substrate, in accordance with oneembodiment of the present disclosure

FIG. 2 is a side cross-sectional view depicting forming a dielectricspacer on a sidewall of at least one fin structure in the plurality offin structures, in accordance with one embodiment of the presentdisclosure.

FIG. 3 is a side cross-sectional view depicting one embodiment offorming a conformal layer of a semiconductor material on the dielectricspacer, the plurality of fin structures and upper surface of bulksubstrate that is present between adjacent fin structures in theplurality of fin structures, in accordance with the present disclosure.

FIG. 4 is a side cross-sectional view depicting one embodiment ofetching the conformal layer of the semiconductor material to providesemiconductor spacers on a sidewall of the dielectric spacer, andetching an exposed portion of the bulk substrate to provide a pedestalportion of the bulk substrate, in accordance with the presentdisclosure.

FIG. 5 is a side cross-sectional view depicting etching the pedestalportion of the fin structures to reduce the width of the pedestalportion to be substantially equal to the width of the upper portion ofthe fin structures, in accordance with one embodiment of the presentdisclosure.

FIG. 6 is a side cross-sectional view depicting forming a dielectricfill in the space between the adjacent fin structures.

FIG. 7 is a side cross-sectional view depicting oxidizing a portion ofthe fin structures that is present below a lower surface of thedielectric spacer, in accordance with one embodiment of the presentdisclosure.

FIG. 8 is a side cross-sectional view depicting recessing the dielectricfill, in accordance with one embodiment of the present disclosure.

FIG. 9 is a side cross-sectional view depicting removing the dielectricspacer from the sidewall of the fin structures.

FIG. 10 is a side cross-sectional view depicting one embodiment of afinFET structure that may be formed using the process flow that isdepicted in FIGS. 1-9, in accordance with the present disclosure.

FIG. 11 is a side cross-sectional view depicting another embodiment of amethod for forming a fin structure, in which a plurality of finstructures are formed from a bulk semiconductor substrate, and a firstdielectric fill is formed in the space between the adjacent finstructures.

FIG. 12 is a side cross-sectional view depicting forming a dielectricspacer on the exposed sidewalls of each fin structure in the pluralityof fin structures that are depicted in FIG. 11, in accordance with oneembodiment of the present disclosure.

FIG. 13 is a side cross-sectional view depicting one embodiment offorming a conformal layer of a semiconductor material on the dielectricspacer, the plurality of fin structures and upper surface of firstdielectric fill that is present between adjacent fin structures of theplurality of fin structures that are depicted in FIG. 12, in accordancewith the present disclosure.

FIG. 14 is a side cross-sectional view depicting one embodiment ofanisotropically etching the conformal layer of the semiconductormaterial to provide semiconductor spacers on a sidewall of thedielectric spacer, in accordance with the present disclosure.

FIG. 15 is a side cross-sectional view depicting forming a seconddielectric fill in the space between the adjacent fin structures on thefirst dielectric fill, in accordance with one embodiment of the presentdisclosure.

FIG. 16 is a side cross-sectional view depicting one embodiment ofoxidizing the semiconductor spacer and a portion of the fin structuresthat is present below a lower surface of the dielectric spacer, inaccordance with the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the claimed structures and methods that maybe embodied in various forms. In addition, each of the examples given inconnection with the various embodiments are intended to be illustrative,and not restrictive. Further, the figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the methods and structures of the present disclosure. Forpurposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the embodiments of the disclosure,as it is oriented in the drawing figures. The term “positioned on” meansthat a first element, such as a first structure, is present on a secondelement, such as a second structure, wherein intervening elements, suchas an interface structure, e.g. interface layer, may be present betweenthe first element and the second element. The term “direct contact”means that a first element, such as a first structure, and a secondelement, such as a second structure, are connected without anyintermediary conducting, insulating or semiconductor layers at theinterface of the two elements.

In some embodiments, the methods and structures disclosed herein form aregion of a dielectric material, e.g., oxide, under a fin structure thatis formed from a bulk semiconductor substrate. As used herein, a “finstructure” refers to a semiconductor material, which can be employed asthe body of a semiconductor device, in which the gate structure ispositioned around the fin structure such that charge flows down thechannel on the two sidewalls of the fin structure and optionally alongthe top surface of the fin structure. In some embodiments, the methodsand structures disclosed herein substantially reduce or eliminatestresses induced in the fin structures from the underlying region of thedielectric material, e.g., oxide, by oxidizing a semiconductor spacerthat is adjacent to the fin structures. Oxidizing the semiconductorspacer produces a compensatory stress that neutralizes the stress beingformed in the fin structures by the underlying region of dielectricmaterial. The methods and structures of the present disclosure are nowdiscussed with more detail referring to FIGS. 1-16.

FIG. 1 depicts one embodiment of forming a plurality of fin structures10 from a bulk semiconductor substrate 5. A “bulk semiconductorsubstrate” is a substrate that is composed of a single semiconductormaterial. A bulk semiconductor substrate 5 does not include a burieddielectric layer that is typically present in silicon on insulator (SOI)substrates. The semiconductor material that provides the bulksemiconductor substrate 5 may be a semiconducting material including,but not limited to silicon, strained silicon, a silicon carbon alloy(e.g., silicon doped with carbon (Si:C), silicon germanium, a silicongermanium and carbon alloy (e.g., silicon germanium doped with carbon(SiGe:C), silicon alloys, germanium, germanium alloys, gallium arsenic,indium arsenic, indium phosphide, as well as other III/V and II/VIcompound semiconductors.

The plurality of fin structures 10 may be formed from the bulksemiconductor substrate 5, using photolithography and etch processes.For example, prior to etching the bulk semiconductor substrate 5 toprovide the plurality of fin structures 10, a layer of the dielectricmaterial is deposited atop the upper surface of the bulk semiconductorsubstrate 5 to provide a dielectric fin cap 15. The material layer thatprovides the dielectric fin cap 15 may be composed of a nitride, oxide,oxynitride material, and/or any other suitable dielectric layer. Thedielectric fin cap 15 may comprise a single layer of dielectric materialor multiple layers of dielectric materials. The material layer thatprovides the dielectric fin cap 15 can be formed by a depositionprocess, such as chemical vapor deposition (CVD) and/or atomic layerdeposition (ALD). Alternatively, the material layer that provides thedielectric fin cap 15 may be formed using a growth process, such asthermal oxidation or thermal nitridation. The material layer thatprovides the dielectric fin cap 15 may have a thickness ranging from 1nm to 100 nm. In one example, the dielectric fin cap 15 is composed ofan oxide, such as SiO₂, that is formed by CVD to a thickness rangingfrom 25 nm to 50 nm.

In one embodiment, following the formation of the layer of dielectricmaterial that provides the dielectric fin cap 15, a photolithography andetch process sequence is applied to the material layer for thedielectric fin cap 15 and the bulk semiconductor substrate 5.Specifically, in one example, a photoresist mask is formed overlying thelayer of the dielectric material that provides dielectric fin cap 15 andis present overlying the bulk semiconductor substrate 5, in which theportion of the dielectric material that is underlying the photoresistmask provides the dielectric fin cap 15, and the portion of the bulksemiconductor substrate 5 that is underlying the photoresist maskprovides the plurality of fin structures 10. The exposed portions of thedielectric material that provides dielectric fin cap 15 and the portionof the bulk semiconductor substrate 5, which are not protected by thephotoresist mask, are removed using a selective etch process. To providethe photoresist mask, a photoresist layer is first positioned on thelayer of the dielectric material that provides dielectric fin cap 15.The photoresist layer may be provided by a blanket layer of photoresistmaterial that is formed utilizing a deposition process such as, e.g.,plasma enhanced CVD (PECVD), evaporation or spin-on coating. The blanketlayer of photoresist material is then patterned to provide thephotoresist mask utilizing a lithographic process that may includeexposing the photoresist material to a pattern of radiation anddeveloping the exposed photoresist material utilizing a resistdeveloper.

Following the formation of the photoresist mask, an etching process mayremove the unprotected portions of the dielectric material that providesthe dielectric fin cap 15 followed by removing a portion of the exposedbulk semiconductor substrate 5 selectively to the photoresist mask. Forexample, the transferring of the pattern provided by the photoresistinto the underlying structures may include an anisotropic etch. As usedherein, an “anisotropic etch process” denotes a material removal processin which the etch rate in the direction normal to the surface to beetched is greater than in the direction parallel to the surface to beetched. The anisotropic etch may include reactive-ion etching (RIE).Other examples of anisotropic etching that can be used at this point ofthe present disclosure include ion beam etching, plasma etching or laserablation. The etch process may be timed to determine the height of thefin structures 10.

Each of the fin structures 10 may have a height H₁ ranging from 5 nm to200 nm. In another embodiment, each of the fin structures 10 has aheight H₁ ranging from 10 nm to 100 nm. In one example, each of the finstructures 10 has a height H₁ ranging from 20 nm to 50 nm. Each of theplurality of fin structures 10 may have a width W₁ of less than 20 nm.In another embodiment, each of the fin structures 10 has a width W₁ranging from 3 nm to 8 nm. Although three fin structures 10 are depictedin FIG. 1, the present disclosure is not limited to only this example.It is noted that any number of fin structures 10 may be formed from thebulk semiconductor substrate 5. The pitch P1 separating adjacent finstructures in the plurality of fin structures 10 may range from 15 nm to200 nm. In another example, the pitch P1 separating adjacent finstructures 10 may range from 15 nm to 100 nm.

FIG. 2 depicts one embodiment of forming a dielectric spacer 20 on asidewall of each fin structure 10. The dielectric spacer 20 typicallyextends across an entirety of a height of the sidewall for each of theplurality of fin structures 10, and in some embodiments may extend ontothe sidewall of the dielectric fin cap 15. The dielectric spacer 20 istypically composed of a dielectric material, such as an oxides (with theexception of silicon oxide), nitrides or oxynitrides (with the exceptionof silicon oxynitride). In some examples, the dielectric spacer 20 maybe composed of hafnium oxide (HfO₂), silicon carbides (SiCN), siliconcarbonitrides, silsequioxanes, siloxanes, boron phosphate silicate glass(BPSG) and combinations thereof.

In one embodiment, the dielectric spacer 20 may be formed by a processsequence that includes depositing a conformal dielectric layer on theplurality of the fin structures 15 and an exposed upper surface of thebulk semiconductor substrate 5 that is present between adjacent finstructures 10. The term “conformal” denotes a layer having a thicknessthat does not deviate from greater than or less than 30% of an averagevalue for the thickness of the layer. In some embodiments, the conformaldielectric layer for forming the dielectric spacer 20 may be formedusing a CVD process, such as PECVD, or the conformal dielectric layermay be deposited using a spin on deposition process. Followingdeposition of the conformal dielectric layer, an anisotropic etchprocess may remove the horizontal portions of the conformal dielectriclayer, wherein the vertical portions of the conformal dielectric layerremain to provide the dielectric spacer 20. The horizontal portions ofthe conformal dielectric layer are the portions of the dialectic layerthat are present on the upper surface of the dielectric fin cap 15 andthe surfaces of the portion of the bulk semiconductor substrate 5 thatare present between adjacent fin structures 10. The anisotropic etchprocess for removing the horizontal portions of the conformal dielectriclayer may be a RIE process. The width of the dielectric spacer 20 mayrange from 3 nm to 15 nm.

FIG. 3 depicts one embodiment of forming a conformal layer of asemiconductor material 25 on the dielectric spacer 20, the dielectricfin cap 15, the plurality of fin structures 10 and upper surface of bulksemiconductor substrate 5 that is present between adjacent finstructures 10. The conformal layer of semiconductor material 25 may becomposed of an amorphous semiconductor material or a multi-crystalline,e.g., polycrystalline, semiconductor material. An amorphoussemiconductor material is a non-crystalline material that lacks thelong-range order characteristic of a crystal. A polycrystallinestructure is a form of semiconductor material made up of randomlyoriented crystallites and containing large-angle grain boundaries, twinboundaries or both. Multi-crystalline is widely referred to apolycrystalline material with large grains (of the order of millimetersto centimeters). The term polycrystalline typically refers to smallgrains (hundreds of nanometers, to hundreds of microns).

In one embodiment, the conformal layer of the semiconductor material 25may be composed of a silicon containing material. Examples ofsilicon-containing materials suitable for the semiconductor materialinclude, but are not limited to, Si, SiGe, SiGeC, SiC, polysilicon,i.e., polySi, amorphous Si, i.e., α:Si, and multi-layers thereof. Thesilicon-containing materials may also include hydrogen, such ashydrogenated silicon (Si:H) or amorphous hydrogenated silicon (α-Si:H).It is noted that the above materials are provided for illustrativepurposes only, and are not intended to limit the present disclosure, asother materials are suitable for provided the conformal layer of thesemiconductor material 25. For example, any semiconductor material thatprovides a strain following oxidation may be suitable for use as thematerial of the conformal layer of the semiconductor material 25 withthe methods and structures of the present disclosure. The conformallayer of the semiconductor material 25 may have a thickness T1 rangingfrom 3 nm to 30 nm. In another embodiment, the conformal layer of thesemiconductor material 25 may have a thickness T1 ranging from 3 nm to10 nm. The conformal layer of the semiconductor material 25 may bedeposited using a CVD process, such as Atmospheric Pressure CVD (APCVD),Low Pressure CVD (LPCVD), Plasma Enhanced CVD (EPCVD), Metal-Organic CVD(MOCVD), atomic layer deposition (ALD) and combinations thereof may alsobe employed.

FIG. 4 depicts one embodiment of etching the conformal layer of thesemiconductor material to provide semiconductor spacers 25 a on asidewall of the dielectric spacer 20, and etching an exposed portion ofthe bulk semiconductor substrate 5 to provide a pedestal portion 30 ofthe bulk semiconductor substrate 5. The etch process for forming thesemiconductor spacers 25 a and the pedestal portion 30 of the bulksemiconductor substrate 5 may be a anisotropic etch, such as RIE, ionbeam etching, plasma etching or laser ablation. The etch process forforming the semiconductor spacers 25 a and the pedestal portion 30 ofthe bulk semiconductor substrate 5 may be an etch that removes thematerial of the semiconductor spacers 25 a and the bulk semiconductorsubstrate 5 selectively to the material of the dielectric fin cap 15. Asused herein, the term “selective” in reference to a material removalprocess denotes that the rate of material removal for a first materialis greater than the rate of removal for at least another material of thestructure to which the material removal process is being applied. Forexample, in one embodiment, a selective etch may include an etchchemistry that removes a first material selectively to a second materialby a ratio of 100:1 or greater, e.g., 1000:1.

In some embodiments, the etch process for forming semiconductor spacers25 a and the pedestal portion 30 of the bulk semiconductor substrate 5is continued until the horizontal portions of the conformal layer of thesemiconductor material are removed in their entirety, and the remainingvertical portions of the conformal layer of the semiconductor materialthat are present on the sidewalls of the dielectric spacer 20 arerecessed so that the height of the semiconductor spacers 25 a is lessthan half the height H1 of the fin structures 10. The portion of thebulk semiconductor substrate 5 that is present between the semiconductorspacers 25 a is etched to provide a trench 35 having a height H2 rangingfrom 10 nm to 200 nm. The depth H2 of the trench 35 defines the heightof the pedestal portion 30 of the fin structures 10.

In one embodiment, the height H4 of the semiconductor spacers 25 aranges from 10 nm to 100 nm. In another embodiment, the height H4 of thesemiconductor spacers 25 a ranges from 20 nm to 50 nm. In oneembodiment, the width W4 of the semiconductor spacers 25 a ranges from 3nm to 30 nm. In yet another embodiment, the width W4 of thesemiconductor spacers 25 a ranges from 3 nm to 10 nm.

FIG. 5 depicts one embodiment of etching the pedestal portion 30 of thefin structures 10 to reduce the width W2 of the pedestal portion 30 tobe substantially equal to the width W1 of the fin structures 10. “Bysubstantially equal” it is meant that the width W2 of the pedestalportion 30 may be within +/−5 nm of the width W1 of the fin structures10. In one embodiment, the pedestal portion 30 may be etched using anisotropic etch. The term “isotropic etch” denotes an etch process thatis non-directional. By “non-directional” it is meant that the etch rateis not substantially greater in any one direction in comparison to allof the etch directions. The isotropic etch may be a wet chemical etch ora dry etch. For example, the etchant may be a corrosive liquid or achemically active ionized gas, such as a plasma. The etch process forreducing the width W2 of the pedestal portion 30 of the fin structures10 may be selective to the semiconductor spacers 25 a, the dielectricspacers 20, and the dielectric fin cap 15. In some embodiments, the stepof etching the pedestal portion 30 of the fin structures 10 may beomitted.

FIG. 6 depicts one embodiment of forming a dielectric fill 35 in thespace between the adjacent fin structures 10 including the trenchesbetween the pedestal portions 30 of the fin structures 10. Although FIG.6 depicts forming the dielectric fill 35 between the adjacent finstructures 10 that are depicted in FIG. 4, the step of forming thedielectric fill 35 is equally applicable to the embodiments of thepresent disclosure that include the step of reducing the width of thepedestal portion 30 of the fin structures 10 as described above withreference to FIG. 5.

Referring to FIG. 6, the dielectric fill 35 may be an oxide containingmaterial. For example, the dielectric fill 35 may be silicon oxide(SiO₂). Other examples of materials that may be employed for thedielectric fill 35 include silicon nitride, silicon oxynitride, hafniumoxide, hafnium oxynitride, alumina and combinations thereof. Thedielectric fill 35 may be formed using CVD, PECVD, high-density plasmaCVD (HPCVD), chemical solution deposition or a spin-on glass process.Following deposition, the material for the dielectric fill 35 may beplanarized so that the upper surface of the dielectric fill is coplanarwith the upper surface of the dielectric fin cap 15.

FIG. 7 depicts oxidizing a portion (hereafter referred to as oxidizedbase portion 40) of the fin structures 10 that is present below a lowersurface of the dielectric spacer 20. During the oxidation of the finstructure 10 to provide the oxidized base portion 40, the semiconductorspacer is also oxidized (hereafter referred to as oxidized semiconductorspacer 25 b). The oxidized base portion 40 produces a first strain andthe oxidized semiconductor spacer 25 b produces a second strain that isopposite the first strain. For example, oxidizing the portion of the finstructures 10 to provide the oxidizing base portion 40 produces anintrinsic strain within the oxidized base portion 40. The term“intrinsic strain” as used herein refers to a stress or presence of astrain, either compressive or tensile, which is developed duringpreparation of a structure and can therefore be retained in thestructure without external force. The mechanical strain can be impartedto the fin structure 10, due to volume expansion of the oxide ascompared with silicon. The intrinsic strain that is present in theoxidized base portion 40 induces a strain on the overlying finstructures 10. Therefore, the direction of the strain is in a direction,i.e., first direction D1, that extends from the base of the finstructure 10 towards an upper surface of the fin structure 10. Theintrinsic strain that is present in the oxidized base portion 40 of thefin structures 10 may range from 0.3 GPa tensile to −0.3 GPa compressivestrain. In the embodiments, in which the pedestal portion 30 is notlaterally etched, the oxidized base portion 40 may have a width W3ranging from 15 nm to 50 nm, and a height H3 ranging from 10 nm to 200nm. In another embodiment, in which the pedestal portion 30 is notlaterally etched, the oxidized base portion 40 may have a width W3ranging from 15 nm to 35 nm, and a height H3 ranging from 35 nm to 70nm.

Substantially simultaneously with the oxidizing of the fin structure 10to provide the oxidized base portion 40, the semiconductor spacer isalso oxidized to form the oxidized semiconductor spacer 25 b, which hasa second strain in a direction D2 opposite to the direction D1 of firststrain produced by the oxidized base portion 40. The strain produced inthe oxidized semiconductor spacer 25 b may be an intrinsic strain. Morespecifically, the intrinsic strain that is present in the oxidizedsemiconductor spacer 25 b may range from 0.3 GPa tensile to −0.3 GPacompressive stress. The oxidized semiconductor spacer 25 b is formed ona sidewall of the fin structure 10 and induces a strain in an oppositedirection, i.e., second direction D2, as the strain being induced by theoxidized base portion 40. For example, the direction of the strain,i.e., second direction D2, induced by the oxidized semiconductor spacer25 b may extend in a direction from the oxidized semiconductor spacer 25b towards the oxidized base portion 40.

The strain produced by the oxidized semiconductor spacer 25 in thesecond direction D2 opposes the strain produced by the oxidized baseportion 40 in the first direction D1 to provide a fin structure 10 thatis substantially relaxed. The substantially relaxed fin structure 10 mayalso be referred to as having a substantially neutral strain state. Insome embodiments, a fin structure that is substantially relaxed is a finstructure 10 having a strain no greater than about +/−0.1 GPa tensile orcompressive. In some embodiments, the strain that can be measured in thefin structure 10 that results from the opposing strains produced by theoxidized semiconductor spacer 25 b and the oxidized base portion 40 mayrange from 0.1 GPa tensile to −0.1 GPa compressive strain. In yetanother embodiment, the strain that can be measured in the fin structure10 that results from the opposing strains produced by the oxidizedsemiconductor spacer 25 b and the oxidized base portion 40 may rangefrom 0.05 GPa tensile to −0.05 GPa compressive strain. In one example,the fin structure 10 may be completely relaxed.

In some embodiments, the oxidation process that produces the oxidizedsemiconductor spacer 25 b and the oxidized base portion 40 may be athermal oxidation process. Typically, the thermal oxidation processincludes annealing in an oxygen containing atmosphere, which may includea hydrogen carrier gas. In some embodiments, the oxidation occurs in afurnace set to a temperature in the range of 900° C. to 1300° C. Inanother embodiment, the oxidation occurs in a furnace set to atemperature in the range of 950° C. to 1200° C. In some embodiments,oxygen from the furnace atmosphere diffuses through the dielectric fill35 to react with the semiconductor material, e.g., silicon, of the bulksemiconductor substrate 5 and the semiconductor spacers 25 a, formingoxide, which includes the oxidized semiconductor spacer 25 b and theoxidized base portion 40 formed at the base of the fin structure 10,leaving an unoxidized portion of the fin structure 10 present betweenthe dielectric fin cap 15 and the oxidized base portion 40. The oxide ofthe oxidized semiconductor spacer 25 b and the oxidized base portion 40may be silicon oxide (SiO₂).

In some embodiments, an oxide region 50 having a triangular-shapedcross-section or tail profile (hereafter referred to as a tail region50) is present at an interface between the unoxidized portion of the finstructure 10 and the oxidized base portion 40 of the fin structure 10.In some embodiments, the tail region 50 may be uniform. As used herein,a “uniform” tail region 50 is a tail region having a height H5 of 5 nmor less. Due to the aforementioned stress balancing between oxidizedsemiconductor spacer 25 and pedestal 30, the amount of mechanical stressis reduced, and tail height H5 is reduced because of the lessstress-enhanced oxidation

During the oxidation process, mechanical stress can be imparted to thefin structure 10, due to volume expansion of the oxide as compared withsilicon. Normally, this could cause the fin structure 10 to mechanicallyshift or tilt, relative to the horizontal, such that the fin structure10 would no longer be perpendicular to the bulk substrate 5. However,due to embodiments of the present disclosure, the dielectric fill 35,being in direct physical contact with the fin structures 10, the finstructure 10 is held firmly in place by the dielectric fill 35 duringthe formation of the oxidized base portion 40, and so the undesirablemechanical shift is prevented.

FIG. 8 depicts one embodiment of recessing the dielectric fill 35. Insome embodiments, the dielectric fill 35 may be recessed using ananisotropic etch process, that removes the material of the dielectricfill 35 selectively to the dielectric fin cap 15. The etch process forrecessing the dielectric fill 35 may also be selective to the dielectricspacers 20. One example of an etch process for recessing the dielectricfill includes RIE. Other examples of anisotropic etching that can beused at this point of the present disclosure include ion beam etching,plasma etching or laser ablation. Typically, the anisotropic etch istimed so that the dielectric fill 35 is recessed to expose thedielectric spacers 20. Typically, the etch process that recessed thedielectric fill 35 will also remove the oxidized semiconductor spacer 25b. In some embodiments, the methods and structures disclosed hereinaddress the stress non-uniformity that occurs during oxidation, thatcauses unbalanced oxidation rates and therefore, non-uniform fin tail.In some embodiments, the fin tail is reduced with a balanced stressprofile along the height.

FIG. 9 depicts one embodiment of removing the dielectric spacer 20 fromthe sidewall of the fin structures 10. The dielectric spacer 20 may beremoved using an etch process that removes the material of thedielectric spacer 20 selectively to the fin structures 10, the remainingportion of the dielectric fill 35 and the tail region 50. The etchprocess for removing the dielectric spacer 20 may be an anisotropicetch, such as RIE. In another embodiment, the etch process for removingthe dielectric spacer 20 may be an isotropic etch, such as a wetchemical etch or a dry etch, e.g., plasma etch. The etch process forremoving the dielectric spacer 20 may also remove the dielectric fin cap15. Removing the dielectric fin cap 15 is optional. Typically, thedielectric fin cap 15 may remain when the fin structure 10 is employedin a fin field effect transistor (finFET), and the dielectric fin cap 15is removed the fin structure 10 is employed in a tri-gate semiconductordevice.

FIG. 10 is a of a finFET structure 100 that may be formed using the finstructure 10 formed by the process flow that is depicted in FIGS. 1-9. A“field effect transistor (FET)” is a semiconductor device in which theoutput current, i.e., source-drain current, is controlled by the voltageapplied to the gate. A FET has three terminals, i.e., gate structure,source region and drain region. A gate structure is a structure used tocontrol output current (i.e., flow of carriers in the channel) of asemiconducting device through electrical or magnetic fields. A finFET isa field effect transistor in which at least the channel portion of thefield effect transistor is present in a fin structure 10. The channel isthe region underlying the gate structure and between the source anddrain of a semiconductor device that becomes conductive when thesemiconductor device is turned on. Although FIG. 10 only depicts twofinFET devices being formed from two fin structures 10, any number offinFET devices may be formed using any number of fin structures 10.

In one embodiment, each of the finFET devices includes a gate structure110 that may be composed of at least one gate dielectric layer 111, atleast one gate conductor layer 112 and at least one gate dielectric cap113. The at least one gate dielectric layer 111 is composed of aninsulator, and is present between the channel region of the finstructure 10 and the at least one gate conductor layer 112 of the gatestructure 110. The gate structure 110 may be formed by forming blanketmaterial layers for the at least one gate dielectric layer 111, the atleast one gate conductor layer 112, and the at least one gate dielectriccap 112 to provide a gate stack, and patterning and etching the gatestack to provide the gate structure 110 utilizing photolithography andetch process steps.

The at least one gate dielectric layer 111 is typically positioned on atleast a portion of the sidewalls of the fin structures 10. The at leastone gate dielectric layer 111 may be formed by a thermal growth processsuch as, e.g., oxidation, nitridation or oxynitridation. In otherembodiments, the at least one gate dielectric layer 111 may be formedusing a deposition process, such as CVD. In some embodiments, the atleast one gate dielectric layer 111 is composed of a low-k dielectricmaterial, such as silicon oxide (SiO₂), which typically has a dielectricconstant of less than 4.0 at room temperature, e.g. 25° C. In someembodiments, the at least one gate dielectric 111 is composed of ahigh-k dielectric material. High-k dielectric materials have adielectric constant greater than silicon oxide (SiO₂) at roomtemperature, e.g., 25° C. For example, a high-k dielectric composed ofhafnium oxide (HFO₂), may have a dielectric constant of 4.0 or greater.

In one embodiment, the at least one gate dielectric layer 111 mayinclude, but is not limited to, an oxide, nitride, oxynitride and/orsilicates including metal silicates, aluminates, titanates and nitrides.In one example, when the at least one gate dielectric layer 11 iscomprised of an oxide, the oxide may be selected from the groupincluding, but not limited to, SiO₂, HfO₂, ZrO₂, Al₂O₃, TiO₂, La₂O₃,SrTiO₃, LaAlO₃, Y₂O₃ and mixture thereof. The physical thickness of theat least one gate dielectric layer 111 may vary, but typically, the atleast one gate dielectric layer 111 has a thickness ranging from 1 nm to10 nm.

The at least one gate conductor layer 112 may be composed ofpolysilicon, SiGe, a silicide, a metal or a metal-silicon-nitride, suchas Ta—Si—N. Examples of metals that can be used as the at least one gateconductor layer 112 include, but are not limited to Al, W, Cu, Ti orother like conductive metals. The physical thickness of the at least onegate conductor layer 112 may range from 1 nm to 10 nm. The gatedielectric cap 113 may be composed of a nitride, oxide, oxynitridematerial, and/or any other suitable dielectric layer.

A gate sidewall spacer 114 may be formed in direct contact with the gatestructure 110. The gate sidewall spacer 114 may be formed usingdeposition and etch processes. The gate sidewall spacer 114 may becomposed of a dielectric material, such as oxides, nitrides oroxynitrides.

Still referring to FIG. 10, a source region 50 and a drain region (notshown as hidden by gate structure in this view) may be formed onopposing sides of the gate structure 110, i.e., on opposing sides of theportion of the fin structure 10 including the channel region. In someembodiments, the source region 50 is a doped region in the finFETdevice, in which majority carriers are flowing into the channel region,and the drain region is a doped region in the finFET device located atthe end of the channel region, in which carriers are flowing out of thefinFET through the drain. N-type finFET devices are produced by dopingthe source region 50 and the drain region with elements from group V ofthe Periodic Table of Elements. In one embodiment, the group V elementis phosphorus, antimony or arsenic. P-type finFET devices are producedby doping the source region 50 and the drain region with elements fromgroup III of the Periodic Table of Elements. In one embodiment, thegroup III element is boron, aluminum, gallium or indium. In oneembodiment, the source region 50 and the drain region are formed by ionimplanting the exposed portions of the fin structures 10 that are onopposing sides of the gate structure 110. In another embodiment, thesource region 50 may be formed by epitaxially forming a p-type or n-typedopant on the exposed portion of the fin structure 10 and driving thedopant from the epitaxially formed material into an extension region ofthe fin structure 10 using an annealing process.

FIGS. 11-16 depict another method for forming a fin structure 10′, inwhich a plurality of fin structures 10′ are formed from a bulksemiconductor substrate 5′. FIG. 10 depicts one embodiment of forming aplurality of fin structure 10′ from a bulk semiconductor substrate 5′,and forming a first dielectric fill 35 a in the space, e.g., trenches,between the adjacent fin structures 10′. The fin structures 10′ that aredepicted in FIG. 11 are similar to the fin structures 10 that aredescribed above with reference to FIG. 1. Therefore, the description ofthe fin structures 10, the bulk substrate 5, and the dielectric cap 15that are depicted in FIG. 1 are suitable for the fin structures 10′, thebulk substrate 5′, and the dielectric cap 15′ that are depicted in FIG.11.

In some embodiments, the first dielectric fill 35 a is deposited in thespace between the adjacent fin structures 10′ using a depositionprocess, such as CVD, and may be recessed by etch process, such as RIE.The first dielectric fill 35 a may be an oxide, nitride or oxynitridematerial. In one example, the first dielectric fill 35 a is composed ofsilicon oxide (SiO₂). It is noted that the above provided compositionsfor the first dielectric fill 35 a are provided for illustrativepurposes only, and that the present disclosure is not intended to belimited thereto. For example, the materials described above for thedielectric fill 35 depicted in FIG. 5 are suitable for the firstdielectric fill 35 a that is depicted in FIG. 11. The etch process forrecessing the first dielectric fill 35 a may be a selective etch processthat removes the material of the dielectric fill 35 a selectively to thedielectric cap 15′. The first dielectric fill 35 a may be recessed untilthe sidewall for the desired height of the fin structure 10′ is exposed.

FIG. 12 depicts one embodiment of forming a dielectric spacer 20′ on theexposed sidewalls of each fin structure 10′ that is depicted in FIG. 11.The description of the dielectric spacer 20 that is depicted in FIG. 2is suitable for one embodiment of the dielectric spacer 20′ that isdepicted in FIG. 12.

FIG. 13 depicts one embodiment of forming a conformal layer of asemiconductor material 25′ on the dielectric spacer 20′, the pluralityof fin structures 10′ and upper surface of first dielectric fill 35 athat is present between the adjacent fin structures 10′ that aredepicted in FIG. 12. The description of the conformal layer of asemiconductor material 25 that is depicted in FIG. 3 is suitable for oneembodiment of the conformal layer of a semiconductor material 25′ thatis depicted in FIG. 13.

FIG. 14 depicts one embodiment of etching the conformal layer of thesemiconductor material to provide semiconductor spacers 25 a′ on asidewall of the dielectric spacer 20′. The etch process for forming thesemiconductor spacers 25 a may be an anisotropic etch, such as RIE, ionbeam etching, plasma etching or laser ablation. The etch process forforming the semiconductor spacers 25 a′ may be an etch that removes thematerial of the semiconductor spacers 25 a′ selectively to the materialof the dielectric cap 15′ and the first dielectric fill 35 a′.

FIG. 15 depicts one embodiment of forming a second dielectric fill 35 bin the space between the adjacent fin structures 10′ on the firstdielectric fill 35 a. The second dielectric fill 35 b may be an oxidecontaining material. For example, the second dielectric fill 35 b may besilicon oxide (SiO₂). Other examples of materials that may be employedfor the second dielectric fill 35 b include silicon nitride, siliconoxynitride, hafnium oxide, hafnium oxynitride, alumina and combinationsthereof. The dielectric fill may be formed using CVD, PECVD,high-density plasma CVD (HPCVD), chemical solution deposition or aspin-on glass process. Following deposition, the material for the seconddielectric fill 35 b may be planarized so that the upper surface of thedielectric fill is coplanar with the upper surface of the dielectric cap15.

FIG. 16 depicts one embodiment of oxidizing the semiconductor spacer toform an oxidized semiconductor spacers 25 b′, and oxidizing a portion ofthe fin structures 10′ that is present below a lower surface of thedielectric spacer 20′ to form an oxidized base portion 40′. Oneembodiment for the oxidation step that provides the oxidizedsemiconductor spacers 25 b′ and the oxidized base portion 40′ isdescribed above with reference to FIG. 7. Similar to the oxidized baseportion 40 and the oxidized semiconductor spacer 25 b that are describedabove and depicted in FIG. 7, the oxidized base portion 40′ that isdepicted in FIG. 16 produces a first strain in a first direction D1′ andthe oxidized semiconductor spacer 25 b that is depicted in FIG. 16produces a second strain in second direction D2′ that is opposite thefirst strain. Therefore, the description of the oxidized semiconductorspacer 25 b, and the second strain produced by the oxidizedsemiconductor spacer 25 b, that are depicted in FIG. 7 is suitable forthe oxidized semiconductor spacer 25 b′ that is depicted in FIG. 16.Further, the description of the oxidized base portion 40, and the firststrain produced by the oxidized base portion 40, that is depicted inFIG. 7 is suitable for the oxidized base portion 40′ that is depicted inFIG. 16.

The strain produced by the oxidized semiconductor spacer 25 b′ in thesecond direction D2′ opposes the strain produced by the oxidized baseportion 40 in the first direction D1′ to provide a fin structure 10′that is substantially relaxed. In some embodiments, the strain that canbe measured in the relaxed fin structure 10′ that results from theopposing strains produced by the oxidized semiconductor spacer 25 b′ andthe oxidized base portion 40′ may range from 0.1 GPa tensile to −0.1 GPacompressive strain. In yet another embodiment, the strain that can bemeasured in the relaxed fin structure 10′ that results from the opposingstrains produced by the oxidized semiconductor spacer 25 b′ and theoxidized base portion 40′ may range from 0.05 GPa tensile to −0.05 GPacompressive strain. In one example, the fin structure 10′ may becompletely relaxed.

In some embodiments, an oxide region 50′ having a triangular-shapedcross-section or tail profile (hereafter referred to as a tail region50) is present at an interface between the unoxidized portion of the finstructure 10′ and the oxidized base portion 40′ of the fin structure10′. In some embodiments, the tail region 50 may have a height H5′ ofless than 5 nm. In a following process sequence, the second dielectricfill 35 b is recessed to expose the dielectric spacers 20′, and thedielectric spacers 20′ are removed. The process sequence for recessingthe second dielectric fill 35 b has been described above for recessingthe dielectric fill 35 that is depicted in FIG. 7. The process sequencefor removing the dielectric spacers 20′ has been described above forremoving the dielectric spacers 20 that are depicted in FIG. 8.

A semiconductor device, such as the finFET structure 100 depicted inFIG. 10 may be formed from the fin structures 10′ that are formed usingthe process sequence described with reference to FIGS. 11-16. Furtherdetails regarding forming the gate structure and the source and drainregions for a finFET structure including the fin structure 10′ formedusing the process sequence depicted in FIGS. 11-16 is described abovewith reference to FIG. 10.

In another embodiment, the process sequence for forming the finFETstructure 100 depicted in FIG. 10 including the fin structures 10 formedusing the method described with reference to FIGS. 1-9 or the finstructures 10′ formed using the method described with reference to FIGS.11-16 includes a gate last process sequence, which is not depicted inthe supplied figures. A gate last process includes forming a replacementgate structure on the channel portion of the fin structures, forming aspacer on the sidewall of the replacement gate structure, forming sourceand drain regions on opposing sides of the replacement gate structure,removing the replacement gate structure, and forming a functional gatestructure in the space once occupied by the replacement gate structure.The replacement gate structure can include sacrificial material thatdefines the geometry of a later formed functional gate structure thatfunctions to switch the semiconductor device from an “on” to “off”state, and vice versa. A process sequence employing a replacement gatestructure may be referred to as a “gate last” process sequence. Bothgate first and gate last process sequences are applicable to the presentdisclosure.

While the present disclosure has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present disclosure. It is therefore intended that the presentdisclosure not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. A method for forming a fin structure comprising:forming a plurality of fin structures from a semiconductor substrate;forming a dielectric spacer on a sidewall of the plurality of finstructures; forming a semiconductor spacer on a sidewall of thedielectric spacer; forming a dielectric fill in a space between adjacentfin structures; and annealing the semiconductor spacer and a portion ofthe plurality of fin structures that is present below a lower surface ofthe dielectric spacer, wherein said annealing the portion of theplurality of fin structures produces a first strain and said annealingthe semiconductor spacer produces a second strain that is opposite thefirst strain.
 2. The method of claim 1, wherein said annealing of thesemiconductor spacer and the portion of the plurality of fin structuresproduces an oxidized semiconductor spacer and an oxidized portion of theplurality of fin structures that is present below the lower surface ofthe dielectric spacer.
 3. The method of claim 1, wherein a magnitude ofthe second strain is substantially equal to a magnitude of the firststrain so that the plurality of fin structures are in a substantiallyneutral strain state.
 4. The method of claim 1, wherein the forming ofthe semiconductor spacer comprises: forming a conformal layer of asemiconductor material on the dielectric spacer, the plurality of finstructures and a upper surface of bulk substrate that is present betweenthe adjacent fin structures in the plurality of fin structures; andanisotropically etching the conformal layer of the semiconductormaterial to form the semiconductor spacer on the sidewall of thedielectric spacer.
 5. The method of claim 1, wherein the semiconductorspacer is comprised of an amorphous silicon containing material or amulti-crystalline silicon containing material.
 6. The method of claim 1,wherein a pedestal portion of a bulk substrate has a width greater thana width of a fin structure of said plurality of fin structures and themethod further comprises etching the pedestal portion of the pluralityof fin structures to reduce the width of the pedestal portion to besubstantially equal to the width of the fin structure.
 7. The method ofclaim 2, wherein said annealing the portion of the plurality of finstructures that is present below the lower surface of the dielectricspacer comprises a thermal oxidation at a temperature ranging from 900°C. to 1300° C.
 8. The method of claim 1 further comprising recessing thedielectric fill to expose the dielectric spacer and removing thedielectric spacer.
 9. The method of claim 8 further comprising: forminga gate structure on a portion of at least one of the plurality of finstructures; forming a source region on said at least one of theplurality of fin structures on a first side of the gate structure; andforming a drain region on said at least one of the plurality of finstructures on a second side of the gate structure.
 10. A method forforming a fin structure comprising: forming a plurality of finstructures from a semiconductor substrate; forming a first dielectricfill in the space between adjacent fin structures of the plurality offin structures, wherein sidewalls of an upper portion of the pluralityof fin structures are exposed; forming a dielectric spacer on thesidewalls of the plurality of fin structure that are exposed; forming asemiconductor spacer on a sidewall of the dielectric spacer; andannealing the semiconductor spacer and a portion of the fin structuresthat is present below a lower surface of the dielectric spacer, whereinsaid annealing the portion of the fin structures produces a first strainand said annealing the semiconductor spacer produces a second strainthat is opposite the first strain.
 11. The method of claim 10, whereinsaid annealing of the semiconductor spacer and the portion of theplurality of fin structures that is present below the lower surface ofthe dielectric spacer produces an oxidized semiconductor spacer and anoxidized portion of the plurality of fin structures that is presentbelow the lower surface of the dielectric spacer.
 12. The method ofclaim 10, wherein a magnitude of the second strain is substantiallyequal to a magnitude of the first strain so that the plurality of finstructures are in a substantially neutral strain state.
 13. The methodof claim 10, wherein said forming the dielectric spacer comprises:depositing a conformal dielectric layer on the plurality of finstructures and an upper surface of the first dielectric fill; andanisotropically etching the conformal dielectric layer to form thedielectric spacer.
 14. The method of claim 10, wherein the semiconductorspacers are comprised of an amorphous silicon containing material or amulti-crystalline silicon containing material.
 15. The method of claim10, wherein the forming of the semiconductor spacer comprises: forming aconformal layer of a semiconductor material on the dielectric spacer,the plurality of fin structures and upper surface of first dielectricfill that is present between the adjacent fin structures of theplurality of fin structures; and anisotropically etching the conformallayer of the semiconductor material to form the semiconductor spacers onthe sidewall of the dielectric spacer.
 16. The method of claim 10,further comprising forming a second dielectric fill in a space betweenthe adjacent fin structures, wherein said forming the second dielectricfill comprises: depositing the second dielectric fill on the firstdielectric fill; and planarizing the second dielectric fill until anupper surface of the plurality of fin structures is coplanar with anupper surface of the dielectric fill.
 17. The method of claim 16,wherein said oxidizing the portion of the plurality of fin structuresthat is present below the lower surface of the dielectric spacercomprises a thermal oxidation at a temperature ranging from 900° C. to1300° C.
 18. The method of claim 10 further comprising: forming a gatestructure on a portion of at least one of the plurality of finstructures; forming a source region on said at least one of theplurality of fin structures on a first side of the gate structure; andforming a drain region on said at least one of the plurality of finstructures on a second side of the gate structure.
 19. A method forforming a fin structure comprising: forming a first spacer on a sidewallof a plurality of fin structures, the first spacer being comprised of adielectric material; forming a second spacer on a sidewall of the firstspacer, the second spacer being comprised of a semiconductor material;forming a dielectric fill in a space between the adjacent finstructures; and annealing the second spacer and a portion of theplurality of fin structures that is present below a lower surface of thefirst spacer, wherein said annealing the portion of the plurality of finstructures produces a first strain and said annealing the second spacerproduces a second strain that is opposite the first strain.